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Wednesday, 15 February 2017

Firing on the Move

Trials to determine accuracy of the T-28 armed with an L-10 gun on the move were performed while driving at a speed of 12-14 kph, firing at a target 800-1000 meters away. The trials were performed in two sets: one with the tank driving towards a 12x10 meter target, the other with the tank driving parallel to a 10x10 meter target. Aiming was done with the PT-1 periscopic sight, firing was done using the foot operated trigger.

While driving towards the target, 14 out of 23 shots hit. While driving parallel to the target, 15 out of 25 shots hit. These results were considered satisfactory.

22 comments:

These are results for a BT-series tank? I've only been able to find a reference to the PT-1 as being a sight for the 45mm.

Not plotting the misses is annoying ... I would really like to know just how far off some of those shots were.

So, thinking about actually shooting at a tank target, assume that you're firing at the side of the target, so we'll pretend that horizontal errors don't matter (most tanks wouldn't be that long, but this works for an approximation). Take 4m as the height of the tank target. Driving toward the target you only lose 6 of the 15 hits, so you're still managing 9 of 25, which is a ridiculously high hit rate. Driving parallel to the target, you lose 9 of 14, so that's only 5 of 23 shots hitting. Much lower, but I'm still surprised that it managed better than 20% hits.

If we also restrict the target to 6m long (a rough average of the T-34, Pz III, and Pz IV, shooting while driving toward the target only loses 2 more hits, so you're still at a respectable 7 of 25. Driving parallel to the target there's no effect because all of the shots that went wide also happened to be low. The distribution of hits forms an odd inverse "T" shape in the second plot, so the small number of shots may be distorting the results.

Anyhow, interesting information. I wonder if the British ever actually did studies like this before the war.

The 2-pounder was a bit different beast as it was *intented* to be fired relatively accurately on the move (Brit doctrine at the time was a little weird), and light enough that the precise aiming adjustments could be left to the gunner's shoulders. IIRC the Japanese (and some interwar US designs) used similar "free-floating" mountings?

British tanks armed with 2pdr practiced continuous aim using manual controll. Due to being a lighter mount, it was more effective under certain conditions of soil and movement than the L10, but never as accurate as firing from static. Firing on the move didn´t really took up traction until the advent of two-axis stabilization.

Firing on the move was a standard part of Soviet tank trials. I have a whole bunch of results aside from these ones. Here's one for example http://tankarchives.blogspot.ca/2013/08/vickers-6-ton-trials.html

Yes it was trialed by everyone. But that doesn´t mean it was practical nor that it was an effective form of combat if the dispersion increased several tenfolds.Continous aim worked well on ships with their predictable roll pattern but not so well on the ground with unpredictable bumps and humps...

Pinpoint accuracy isn't exactly important in area suppression fire, though. Infantrymen on the average care preciously little about the statistics when stuff starts exploding in the vicinity and fragments and bullets are buzzing around their ears...

The stability came at the cost of a suspension that limited the top speed. There was a project to make a T-28 with a Christie suspension (T-29). The tank was a lot faster, but not as stable on the move.

The accuracy is such that firing on the move should not be considered practical. The 50% zone cannot be established due to too many wild shots missing the target at all (39% and 42%, respectively).Out of those remaining which managed to actually hit the 120m^2 and 100m^2 oversized target (compared with only 10-20m^2 area for an actual tank sized target), the probable error is larger than a tank sized target.

As critical mass says, the error space is huge, really very little chance of hitting a tank, certainly compared to a stationary tank firing back at a T28 at 800m. However, for HE fire it might be more acceptable, although the dispersion is still large.

They wouldn't be shooting at a tank, realistically. The T-28 was an infantry support tank, and it would be firing at infantry positions as a part of at least a platoon of tanks. That is why such a high dispersion is considered acceptable.

For area suppression with HE that certainly sounds sufficient - and bringing the tank to a halt from that speed isn't going to take long if more accurate fire is required for "point targets" (MG nests or whatever).

I don't understand why you would bother firing at an area target on the move, especially moving parallel to the target.

Actually, it sort of makes sense if you still think in terms of drive-bys and breaking right through a defensive line while shooting in all directions (multi-turreted tank). Poor tactical concepts, mostly.

Defenses aren't just lines. They are more complicated shapes, where the next line of defense isn't guaranteed to be parallel to the one that you just broke through or perpendicular to the direction you're going.

And sometimes you just need to suppress an area while maneuvering towards a different location entirely. Since you have a 360-degree arc of fire on the main turret might as well put it to use, plus the testers would be doing a poor job if they didn't trial that kind of scenario already for the sake of reference anyway.

In 1938 the BT-7 was tested with a TOS sight with gyroscope stabilization. I would of thought one way to test it would be to compare it to a control shoot without the stabilization. Of course the same tank and gun should be used so the benefit of stabilization could be determined.

Put it into perspective. The mean hitting area at 1000m for a L10 gun fired from T28 was 2.09m^2 stationary. On the move, the dispersion according to these data is approx. 50 times larger. Under the stress of combat, rather than prooving ground conditions, that won´t get smaller. You will not be able to hit a large house consistently except for an isolated hit here and there You jointly happen to witness. Pointing errors are the main cause of dispersion under fire at move conditions.